Due to the recent energy problems that have arisen, considerable interest has been given to wind power to be converted efficiently into electrical energy. Most of the developments and advancements have been focused on the improvement of the aerodynamics of propeller-type turbines, e.g., known as wind turbines and initially referred to as windmills. Typically, each turbine-generator system is mounted on the top of a tall tower, where the taller the tower, the higher the prevailing wind speed. The electrical power generated from a wind turbine is proportional to cubic order of the wind speed. Furthermore, the longer each turbine blade, the higher the power generation is. However, long blades are costly, can be subjected to defects and failure, take up a large amount of space, and generate excessive noise and vibration. The electrical power generated from a wind turbine is directly proportional to the square of the propeller length. However, taller towers and longer propellers increase not only the cost of material and installation, but also the cost of maintenance.
The current wind power generation systems typically suffer from low efficiency, high capital cost, unpredictable failures, excessively high noise and vibration, and/or high maintenance. Due to higher wind speed, large wind farms have recently been installed at sea. These sea-based systems suffer from even much higher capital and maintenance costs. Therefore, the growth of wind farms has been slow at best.
One of the national goals is that wind energy must provide 20% of the nation's electricity by the year 2030. This level of wind power will support 500,000 jobs while saving the consumers $128 billion by lowering the price of natural gas. In addition, it will cut greenhouse gas emission that is equivalent to taking 140,000,000 cars off the road. While no breakthrough in wind power technology is needed to achieve this goal, power transmission lines, reliability, reduction of operation and maintenance costs, and reduction of downtime and failure of wind turbines is crucial.
The operational and maintenance costs of wind turbines should be reduced to make conversion of wind energy to electrical power economically more viable. The wind turbines must also become more reliable with reduced downtime and failures. For example, for offshore wind turbines, the costs for operation and maintenance are estimated in the order of 30 to 35% of the costs of electricity. Roughly 25% to 35% is related to preventive maintenance while 65% to 75% is due to corrective maintenance.
Wind turbines are complex machines with several sub-machines that convert the kinetic energy of moving air to electrical power. Extraction of a significant amount of energy requires high wind speeds and large turbine diameters. In general, turbine speeds are slow (about 20 rpm) and the speed must be increased to a useful generator speed. A typical wind machine has a 3-blade turbine of more than 60 meters in diameter. This turbine drives a generator through a speed-increasing gearbox that generally has a planetary first stage and one or two additional parallel shaft stages. The generator runs at about 1500 rpm and produces about 1.5 MW. Many wind turbines are variable speed machines; the speed depends on the wind conditions and can vary over a wide range. For these machines, high power output requires high levels of torque and accompanying high gear-mesh forces. Because of the low speed of the turbine, the various gearbox components are usually supported by rolling element bearings. These bearings are subject to significant radial loads and need to be carefully monitored to detect any degradation.
At present, with the increasing installed power of the wind turbines, the application of offshore wind turbines, and major problems with turbine blades and gearboxes, the necessity of condition monitoring can no longer be neglected. Some components, although designed for the turbine lifetime, may require repair or fail earlier than expected. This is emphasized by the approach of warranty and insurance companies that simply require application of monitoring provisions. Otherwise, expensive preventive replacements or inspections should be carried out periodically.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternatives to existing wind power generation systems.